The proposed studies will elucidate the roles of five genes and their protein products in the development of brain and behavior. They focus on sexual differentiation of the structure and function of the song control system in the forebrain of zebra finches. Only males sing, and the brain areas that control song are far larger in males, which is due to males having more and larger cells in these regions than females. In many vertebrates, the development of these types of male-biased differences in behavior and morphology is regulated mainly by gonadal steroids. However, in some mammalian systems, sexual differentiation is controlled more directly by the expression of genes. In zebra finches, the evidence suggests that both are involved. The present proposal will test the hypothesis that masculinization of the zebra finch song system is controlled by genes, including those on the Z-chromosome (unlike XX/XY mammals, male zebra finches are ZZ and females are ZW), that influence the response of the brain to steroid hormones. The work involves characterization of five genes we recently identified in the zebra finch brain with enhanced expression in song control nuclei in males compared to females. These genes include those encoding ribosomal proteins L17 and L37, secretory carrier membrane protein 1 (SCAMP1), zinc finger protein 216 (ZNF216) and a COBW-domain containing protein. We will complete the sequence analysis for these genes, confirm their locations on zebra finch chromosomes, and determine the time-course of their sexually dimorphic expression within the song circuit and related regions. The effects of inhibiting their function on development of song learning and masculinization of song system morphology will be elucidated. In addition, interactions between the genes and steroid hormone will be investigated. For example, the role of estradiol in the expression of the genes and potential interactions with androgen receptors, both of which are involved in masculinization, will be studied. Very little information is available in the literature on these genes, so as this work is pursued, we will learn not only more about mechanisms regulating sexual differentiation, but also about the genes themselves. Most importantly, however, the proposed studies will elucidate mechanisms critical for normal development of brain structure and function, and can lead to the discovery of solutions to problems, including those associated with disease, injury, aging and contaminant exposure.